(1) Field of the Invention
The present invention relates to an acquisition system associated with towed array, spherical array, and hull array trackers, and more specifically, to an acquisition system that provides relatively accurate estimates of initial values of bearing rate and signal-to-noise ratios making the acquisition system particularly suited for tracking targets having high bearing rates.
(2) Description of the Prior Art
Acquisition systems, such as those used for sea and underwater detection employing towed array trackers, spherical array trackers or hully array trackers that track a target commonly employ recursive routines for establishing the initial parameters of the target. Recursive trackers, which include bearing trackers, such as alpha-beta and Kalman, require initial values of all states that will be updated as new data arrives. An alpha-beta recursive tracker is more fully described in the technical article of T. Benedict and G. Bordner, “Synthesis of an Optimal Set of Radar Track-While-Scan Smoothing Equations,” Institute of Radio Engineers Transactions on Automatic Control, AC-7, Jul. 1962, pp 27–32. The Kalman recursive tracker is more fully described in the book by A. Gelb, Chapter 4, Applied Optimal Estimation, Mass. Institute of Technology Press, Cambridge, Mass., 1974.
For all recursive trackers, the closer the initial values are to the actual values, the higher the probability that the tracker, in particular the bearing tracker, will successfully acquire (i.e., begin following) the target. States requiring initialization for modern narrowband trackers are bearing, bearing rate, frequency, frequency rate, and signal-to-noise ratio (SNR). Initial values for bearing and frequency are readily available if an operator, such as the tracker operator, clicks on a line that he has observed on a beam's spectragram (gram). The initial bearing can be set equal to the steering angle of the beam whose gram was clicked, and the initial frequency can be set equal to the center frequency of the fast Fourier transform (FFT) bin containing the clicked point on the gram. Initial values for bearing rate, frequency rate, and SNR, however, are not readily available; they, therefore, are usually set to default values. The typical default value used for bearing rate is zero. This default setting of zero frequently results in a failure to acquire targets that have high bearing rates, i.e., rates significantly different from zero. It is desired that an acquisition system be provided that provides initial values for bearing rate and SNR, so as to more readily acquire targets that have high bearing rates.